Why is parameter in contravariant position?

Question

I\'m trying to use a covariant type parameter inside a trait to construct a case-class like so:

trait MyTrait[+T] {
  private case class MyClass(c: T)
}
         


        

Answer 1

Almost there. Here:

scala> trait MyTrait[+T] {
     |   private case class MyClass[U >: T](c: U)
     | }
defined trait MyTrait

Which means MyClass[Any] is valid for all T. That is at the root of why one cannot use T in that position, but demonstrating it requires more code than I'm in the mood for at the moment. :-)